This invention relates to forming flanges on a drawn and ironed (D&I) container, and in particular, to the so-called two piece beverage can and the tool used for putting a flange on the partially formed container. D&I refers to the process used to manufacture the container. A shallow metal cup is drawn from a thin metal sheet and then punched through a plurality of ironing rings which thin the wall without substantially reducing the diameter. During this process the wall of the container is reduced to about one third of its original thickness, thus leaving a cylindrical container open at one end with a thinner wall than the bottom. The open end is trimmed to be the right length and to be square with respect to the axis of the container. It is at this stage that the container is first necked then flanged, so that the container can be double seamed with an end during a closure process after filling.
D&I containers are generally made out of aluminum or tinplated steel; during the ironing process the metal is substantially worked, particularly in the sidewall, and thus the hardness of the material increases and its ductility decreases. Consequently, there is a potential for the metal to be overworked, to the point of failure. One mode of failure is the cracking of the outer periphery of the flange. More particularly, a radial crack occurs in areas of the flange where the metal has an inclusion or a weak point.
For many years containers have been drawn and ironed from low temper (T.sub.1 and T.sub.2) box annealed tinplate steel. This metal has operated successfully in providing the required combination of strength, hardness and ductility such that flange cracked cans could easily be kept below a predetermined number per thousand. It has been found to be desirable to use higher temper metals to manufacture D&1 containers. These higher temper materials can be used in lighter gauges, such that the number of containers which can be made per pound of steel are greater, and yet the performance and strength of the container so produced is equivalent to or better than the heavier gauge cans.
In experimenting with higher temper materials of light gauge, it has been found that the D&I process can be applied without much difficulty, except in the area of flange cracking. Techniques for overcoming the flange cracking problem include re-annealing before flanging, flanging to a shorter flange length or angle, and the like. All of these approaches have their disadvantages and limitations.
The present method of flanging uses a commercial flanging head having cones carried to rotate about their axes parallel to the axis of rotation of the total head. The tool is carried on a necker flanger machine, and is brought into the open end of the trimmed D&I container. The cones are rolled and moved against the upper inside edge of the container in such a way that the flange is flared outwardly to give the necessary configuration for an effective double seam. Use of this type of commercially available flanging head has produced about three times as many cracked flanges per thousand containers with higher temper materials as with the low temper steels or the softer aluminums.